Enhancing anti-tumor T cell function and inducing T cell proliferation is a powerful and new approach for cancer treatment. Three immune-oncology antibodies (e.g., immuno-modulators) are presently marketed. Anti-CTLA-4 (YERVOY/ipilimumab) is thought to augment immune responses at the point of T cell priming and anti-PD-1 antibodies (OPDIVO/nivolumab and KEYTRUDA/pembrolizumab) are thought to act in the local tumor microenvironment, by relieving an inhibitory checkpoint in tumor specific T cells that have already been primed and activated.
ICOS is a co-stimulatory T cell receptor with structural and functional relation to the CD28/CTLA-4-1g superfamily (Hutloff, et al., “ICOS is an inducible T-cell co-stimulator structurally and functionally related to CD28”, Nature, 397:263-266 (1999)). Activation of ICOS occurs through binding by ICOS-L (B7RP-1/B7-H2). Neither B7-1 nor B7-2 (ligands for CD28 and CTLA4) bind or activate ICOS. However, ICOS-L has been shown to bind weakly to both CD28 and CTLA-4 (Yao S et al., “B7-H2 is a costimulatory ligand for CD28 in human”, Immunity, 34(5); 729-40 (2011)). Expression of ICOS appears to be restricted to T cells. ICOS expression levels vary between different T cell subsets and on T cell activation status. ICOS expression has been shown on resting TH17, T follicular helper (TFH) and regulatory T (Treg) cells; however, unlike CD28; it is not highly expressed on naïve TH1 and TH2 effector T cell populations (Paulos C M et al., “The inducible costimulator (ICOS) is critical for the development of human Th17 cells”, Sci Transl Med, 2(55); 55ra78 (2010)). ICOS expression is highly induced on CD4+ and CD8+ effector T cells following activation through TCR engagement (Wakamatsu E, et al., “Convergent and divergent effects of costimulatory molecules in conventional and regulatory CD4+ T cells”, Proc Natal Acad Sci USA, 110(3); 1023-8 (2013)). Co-stimulatory signalling through ICOS receptor only occurs in T cells receiving a concurrent TCR activation signal (Sharpe A H and Freeman G J. “The B7-CD28 Superfamily”, Nat. Rev Immunol, 2(2); 116-26 (2002)). In activated antigen specific T cells, ICOS regulates the production of both TH1 and TH2 cytokines including IFN-γ, TNF-α, IL-10, IL-4, IL-13 and others. ICOS also stimulates effector T cell proliferation, albeit to a lesser extent than CD28 (Sharpe A H and Freeman G J. “The B7-CD28 Superfamily”, Nat. Rev Immunol, 2(2); 116-26 (2002))
A growing body of literature supports the idea that activating ICOS on CD4+ and CD8+ effector T cells has anti-tumor potential. An ICOS-L-Fc fusion protein caused tumor growth delay and complete tumor eradication in mice with SA-1 (sarcoma), Meth A (fibrosarcoma), EMT6 (breast) and P815 (mastocytoma) and EL-4 (plasmacytoma) syngeneic tumors, whereas no activity was observed in the B16-F10 (melanoma) tumor model which is known to be poorly immunogenic (Ara G et al., “Potent activity of soluble B7RP-1-Fc in therapy of murine tumors in syngeneic hosts”, Int. J Cancer, 103(4); 501-7 (2003)). The anti-tumor activity of ICOS-L-Fc was dependent upon an intact immune response, as the activity was completely lost in tumors grown in nude mice. Analysis of tumors from ICOS-L-Fc treated mice demonstrated a significant increase in CD4+ and CD8+ T cell infiltration in tumors responsive to treatment, supporting the immunostimulatory effect of ICOS-L-Fc in these models.
Another report using ICOS−/− and ICOS-L−/− mice demonstrated the requirement of ICOS signalling in mediating the anti-tumor activity of an anti-CTLA4 antibody in the B16/B16 melanoma syngeneic tumor model (Fu T et al., “The ICOS/ICOSL pathway is required for optimal antitumor responses mediated by anti-CTLA-4 therapy”, Cancer Res, 71(16); 5445-54 (2011)). Mice lacking ICOS or ICOS-L had significantly decreased survival rates as compared to wild-type mice after anti-CTLA4 antibody treatment. In a separate study, B16/B16 tumor cells were transduced to overexpress recombinant murine ICOS-L. These tumors were found to be significantly more sensitive to anti-CTLA4 treatment as compared to a B16/B16 tumor cells transduced with a control protein (Allison J et al., “Combination immunotherapy for the treatment of cancer”, WO2011/041613 A2 (2009)). These studies provide evidence of the anti-tumor potential of an ICOS agonist, both alone and in combination with other immunomodulatory antibodies.
Emerging data from patients treated with anti-CTLA4 antibodies also point to the positive role of ICOS+ effector T cells in mediating an anti-tumor immune response. Patients with metastatic melanoma (Giacomo A M D et al., “Long-term survival and immunological parameters in metastatic melanoma patients who respond to ipilimumab 10 mg/kg within an expanded access program”, Cancer Immunol Immunother., 62(6); 1021-8 (2013)); urothelial (Carthon B C et al., “Preoperative CTLA-4 blockade: Tolerability and immune monitoring in the setting of a presurgical clinical trial” Clin Cancer Res., 16(10); 2861-71 (2010)); breast (Vonderheide R H et al., “Tremelimumab in combination with exemestane in patients with advanced breast cancer and treatment-associated modulation of inducible costimulator expression on patient T cells”, Clin Cancer Res., 16(13); 3485-94 (2010)); and prostate cancer which have increased absolute counts of circulating and tumor infiltrating CD4+ICOS+ and CD8+ICOS+ T cells after ipilimumab treatment have significantly better treatment related outcomes than patients where little or no increases are observed. Importantly, it was shown that ipilimumab changes the ICOS+ T effector:Treg ratio, reversing an abundance of Tregs pre-treatment to a significant abundance of T effectors vs. Tregs following treatment (Liakou C I et al., “CTLA-4 blockade increases IFN-gamma producing CD4+ICOShi cells to shift the ratio of effector to regulatory T cells in cancer patients”, Proc Natl Acad Sci USA. 105(39); 14987-92 (2008)) and (Vonderheide R H et al., Clin Cancer Res., 16(13); 3485-94 (2010)). Therefore, ICOS positive T effector cells are a positive predictive biomarker of ipilimumab response which points to the potential advantage of activating this population of cells with an agonist ICOS antibody.
Thus, there is a need for additional T cell proliferation inducing molecules in the treatment of cancer.